Mechanism for controlling the tension in conductors during stringing



May 7, 1968 w. BETTA 3,381,938

MECHANISM FOR CONTROLLING THE TENSION IN CONDUCTORS DURING STRINGING Filed Sept. 29, 1965 5 Sheets-Sheet l Inventor ttorn e ys May 7, 1968 BETTA 3,381,938

MECHANISM FOR C ROLLING T ION IN CONDUCTORS DURING S ING 5 Sheets-Sheet Filed Sept. 29, 1965 May 7, 1968 w. BETTA MECHANISM FOR CONTROLLING THE TENSION IN CONDUCTORS DURING STRINGING 3 Sheets-Sheet 5 Filed Sept. 29, 1965 Inventor B eTTw Wal'f'eY B J T A Horn e y United States Patent 3,381,938 MECHANISM FOR CONTROLLING THE TENSION IN CONDUCTORS DURING STRINGING Walter Betta, Milan, Italy, assignor to C.R.F. Qfiicine Meceaniche di Precisions S.p.A., Milan, Italy, a company of Italy Filed Sept. 29, 1965, Ser. No. 491,358 Claims priority, application Italy, Sept. 29, 1964, 51,788, Patent 738,605 9 Claims. (Cl. 254-1343) ABSTRACT OF THE DISCLGdURE A device for balancing the tension of two pairs of cables as they are fed out from a feed drum \by means of a drawing rope, said device including a body member secured to the drawing rope and having a pair of pulleys mounted therein. Each pulley has a loop of rope extending thereover, the ends of each of the ropes being secured to two cables of the same pair, the pulleys thus enabling, through the action of their associated loop, an equal stretch of each cable when the drawing rope is pulled away from said feed drum. Also provided are two braking drums, each having a pair of cables passing thereover in frictional engagement therewith, along with means for equally braking the drums to maintain equal tension in the pairs of cables.

In order to resolve certain electrical problems, designers of modern high tension and very high tension lines have in recent years turned to the use of a plurality of conductors per phase. From this idea has emerged the problem of providing a system for stretching the said conductors, which whilst fulfilling the known requirements of stretching under mechanical tension (this method ensuring the best conservation of the conductors) is at the same time the most economical system possible.

Much experience in this field has established that the most economical method of effecting the stretching of a bundle of conductors is that which involves the use of a single drawing rope, thereby effecting the simultaneous stretching of all the conductors in the bundle. In order to carry out this method of stretching it is absolutely essential:

(1) That the tensions in the individual conductors of the bundle should be kept always equal to one another: it is in fact the one condition that ensures that the distance of all the conductors from the ground is that which was intended by the designer.

(2) That the element connecting the rope and the conductors should pass smoothly over the pulleys employed for stringing, causing as little increase in tension as possible during its passage.

The apparatus according to the present invention meets all these requirements well. The invention permits the automatic simultaneous unwinding, under constant tension, of at least four conductors by means of a single drawing rope, and it comprises adhesion means, with controlled braking, set in rotation by the conductors that pass over it, and hydrodynamic means for controlling the braking. The said apparatus is characterised by the feature that each group of the said adhesion means has associated with it a pair of cables and the said hydrodynamic means provide a differential control of the braking coupling acting on each group of adhesion means, in such manner as to balance the tension between the individual pairs of cables, means also being provided in association with the connection between drawing rope and cables for balancing the tension between the two cables of each pair.

In accordance with a further feature of the present invention the said means associated with the connection between drawing rope and conductors for balancing the tension between the conductors of each pair are constituted by a substantially flat housing provided with systems of freely rotatable pulleys with. each of which is associated a pair of conductors.

In accordance with a further feature of the present invention there is also provided a multiple sheave which can be associated with each pole of the line, which provides pulleys for the drawing rope and the conductors and is particularly adapted to permit the passage of the said connection with a very much reduced increase of tension. With this object, the multiple sheave includes pulleys of large diameter for the conductors and a pulley of appreciably smaller diameter for the passage of the drawing rope, this pulley being disposed in a forward position, in the direction in which the cable is pulled, relative to the principal axis of the multiple sheave, with its periphery above the level of the periphery of the pulleys of large diameter.

The invention will now be described by way of example with reference to the accompanying drawings, in which:

FIG. 1 is a plan View of the complex of braking apparatus,

FIG. 2 is a section on the line 11-11 of FIG. 1,

FIG. 3 is a section on the line IlI-Ill of FIG. 1,

FIG. 4 is a diagrammatic view of the hydrodynamic circuit for controlling the apparatus of FIG. 1,

FIG. 5 is a perspective view of a connecting group for four conductors,

FIG. 6 is a front view of a multiple sheave for the passage of four conductors and the drawing rope, and

FIG. 7 is a side view of the multiple sheave.

As shown in FIGS. 1 and 2, the braking apparatus for four conductors 1, 2, 3, 4 consists essentially of two groups of drums T and T Each group of drums is constituted, as shown in FIG. 3, by wheels 5, 6 and 7 of large diameter. The wheels 5 and 7' are solid with the hub 8 and can rotate freely via this hub and rolling bearings 9 on a supporting shaft 10. On the central part of the hub 3 the wheel 6 can rotate on bearings 11. The wheel 6 is provided on one side with a ring of teeth 12. A ring of teeth 13 is also associated with the wheel 5. By means of the rings of teeth 12 and 13 the rotation of the wheels 5-7 and 6 is transmitted respectively to pinions 14 and 15. The wheels 5-7 and 6 have on their peripheries grooves in which the cables 1, 2, 3 and 4- wind. More precisely the cable 1 winds in the groove of wheel 5, the cable 4 in the groove of wheel 7 and the cables 2 and 3 wind on the wheel 6, starting from its opposite ends.

The wheels 57 and 6 of the two groups T and T constitute the above mentioned adhesion means for braking the cables 1, 2, 3 and 4, whilst the braking proper is effected by means of the group illustrated in FIG. 4. The shafts 1 and 15" of this group are solid respectively with the pinions 14 and 15. They control the hydrodynamic groups for controlling the braking, indicated respectively at I and l, which will be described below.

The shaft 14' actuates, when rotating, a reversible volumetric hydraulic pump 16 which supplies fluid, generally oil, from a reservoir 17 via a filter 18. This fluid is fed via a pipe 19 to the main control valve 26 under constant pressure. The fluid in the front chamber 21 of the piston 22 then traverses pipe 23 and passes to the rear chamber 24 in which is located a return spring 25. From this chamber the fluid passes via a pipe 26 and a non-return valve 26' to a pilot valve 27 for controlling the pressure of the valve 2%.

When the piston 22 is in the forward position the fluid passes through the pipe 28 to chamber 29 from which it passes via a pipe 3% to actuate a hydraulic motor 31 for driving a blower 32. The latter serves to create a cooling current in the heat exchanger 33. The part of the fluid not fed to the motor 31 passes into chamber 34 and, pressing the piston 35 against the action of the spring 36, flows via the pipe 37 so as to pass through the piping 33 to the heat exchanger 33. To this latter is also fed, via piping 39, the output of the hydraulic motor 31. Piping 49 connects the chamber 24 to the chamber 41 that accommodates spring 36, so that these two chambers are maintained under the same pressure. Group I is wholly identical with group I just described and is also associated, via piping 42 with non-return valve 42., with the above mentioned pilot valve 27. In this manner, control of all the groups is effected by means of a single valve.

Directly at the outlet of both volumetric pumps 16 is connected a pipe 43 the purpose of which is to equalize the pressure in the two groups as will be described below. The pressures in the two groups are further indicated and controlled by means of manometers 44.

During operation, if the torques applied to the shafts 14 and 15' are equal, the two circuits operate in identical manner, as described, and the hydraulic pump 16, feeds part of the fluid to the motor 31 whilst part fiow by via the passage 37 and is supplied to the heat exchanger 33. From here, the fluid passes to the reservoir 17 where it is again drawn by the pump 1e.

When the pressures in the two circuits are identical the non-return valves 26' and 42' are open, and a certain quantity of fluid flows to the pilot valve 27, then passing to the output via the piping 27'. In the return piping 43 there is no flow of fluid, since the pressures at the ends thereof are equal.

In the event of unbalance occurring between the torques in the shafts l4 and 15', the valve 4-2 and piping 43 immediately come into operation. Assuming for example that the greater torque is exerted on the shaft 14' due to a higher pressure in group I, the valve 42 closes the piping 42. whilst a certain quantity of fluid passes via the piping 43 from the group I to the group J'. This condition persists until the same pressure as that in group I is established in group I, signifying that a torque equal to that exerted on shaft 14" is exerted on shaft 15. In other words, it may be said that the fluid that passes through the piping 43, flowing in a direction opposite to the output of the pump 16 driven by shaft 15, tends to brake the shaft 15' and equalise the two torque values.

At the limit, given that the hydraulic pumps 16 are reversible, if the torque exerted on the shaft 15' becomes zero, the oil under pressure fed by the pump 16 controlled by the shaft 14 feeds via the piping 43 the pump 16 of the shaft 15 which operates as a hydraulic motor to transmit an opposite torque to the shaft 15.

In this manner, therefore the torques exerted on the wheels -7 and 6 respectively, or the tensions on the pairs of cables L4, and 245 respectively are maintained con stantly equal during the stringing operation.

Since there must of course be equilibrium between the tensions in the two cables 2 and 3 wound on the wheel 6 and the tensions in the two cables l and 4 wound on the wheels 5 and 7 respectively, there is provided for this purpose a particular type of connection between the drawing rope and these cables. This connection is clearly illustrated in FIG. 5, in which it can be seen that the cables 2 and 3 are connected to a loop of rope passing around pulley 46 which is freely rotatable on a pin 47. The cables 1 and 4 are also associated with a loop of rope 45 which passes round pulleys 4-8 freely rotatable on respective pins 49. The pins a7 and 49 are solid with the connecting box 56 to which is connected the drawing rope 51 via a rotary connection 52. The object of the rotary connection 52; is to avoid the transmission of any torsion accumulated in the drawing rope to the connection box 59. Similar rotatable connections 53 are provided for connecting the cables 1, 2 and 3, 4 to the respective loops and 45' so as to prevent the transmission of torque accumulated in the cables to the box 50.

In order to stabilise the connecting box it is also particularly useful to employ counterweights 54.

The presence of the box 50 of relatively large dimensions, has necessitated the study of a particular type of multiple sheave for association with the poles of the line, which permits smooth passage. With sheaves of known type, in fact, at the instant of passage of the connection there is an appreciable increase in tension that ceases suddenly when the connection has passed, producing unbalance and oscillations in all the lines, with great danger to the endurance of the structure. The multiple sheave according to the present invention, illustrated in FIGS. 6 and 7, comprises, essentially four pulleys 55, of large diameter for the cables to be stretched and a central pulley 56 for the drawing rope. The pulley $6 is mounted in a forward position in the direction in which the cables are drawn, relative to the principal axis x-x of the sheave, and with its periphery slightly above the level of the periphery of the pulleys 55. Due to this construction, at the instant of passage of the box 50 on to the sheave the axis of instantaneous rotation of the system is located at point A wherein the lines yy and zz meet, along which are exerted respectively the normal traction and resistance forces. This means that the radius of the ideal pulley over which the box 50 passes may be regarded as effectively longer than the radius of the pulleys 5 5, and this obviously represents an advantage from the point of view of ease of transit.

The multiple sheave also includes guiding means associated with the pulley 56, to ensure that the drawing rope is guided with certainty in the groove 56'. The said means are constituted essentially by metallic half-rings 57 facing the rim of the pulley 56 and solid with arms 58 which permit them to lift, by rotation about pin 59, at the instant of passage of the connection box 50 onto the multiple sheave.

The said guiding means are completed by a pair of rods 60, disposed on opposite sides of the path of the drawing rope, the object of the rods 60 being mainly to maintain the multiple sheave in perfect alignment with the said drawing rope.

It will be understood that the invention is not limited to the apparatus illustrated but that numerous variants may be applied to the various parts that it comprises, particularly for the purpose of permitting the stringing of more than two pairs of cables, without thereby exceeding the scope of the invention.

What I claim is:

1. A device for balancing the tension of two pairs of cables as they are fed out from a feed drum by means of a drawing rope, said device comprising first connection means for connecting said drawing rope to said four cables and comprising a body means connected to said drawing rope, two loops of rope each connected at their ends to two cables of the same pair, and at least one pulley associated with each loop, each pulley being freely mounted for rotation on said body means and engaging its associated loop, said pulleys enabling, through the action of the associated loop, an equal stretch of each cable when said drawing rope is pulled away from said feed drum; two braking drums each having a pair of cables passing thereover in frictional engagement therewith; and a balanced hydraulic system for equally braking said drums to maintain equal tension in said pairs of cables, said hydraulic system comprising a pair of axles, each operatively connected to a corresponding drum, a volumetric fluid pump operatively connected to said axle, fluid conduit means for supplying fluid to, and receiving fluid from, said pump, said conduit means adapted to brake the -fi0w of said fluid to control the braking of said drum through said pump, and second connecting means connecting the output of said pumps for equalizing said fluid braking pressure.

2. A device according to claim 1, in which said fluid conduit means includes a main circuit with incompressible fluid; a non-return valve mounted in said circuit; a pilot valve for controlling the braking pressure of said fluid; and a heat exchanger mounted in said circuit for cooling said fluid.

3. A device according to claim 2, in which the pressure in both circuits is controlled by one single common pilot valve.

4. A device according to claim 2, in which said conduit means further includes a secondary circuit; a blower for refrigerating the fluid circulating in the heat exchanger, and means responsive to the pressure of the fluid flowing in said secondary circuit to actuate said blower.

5. A device according to claim \1, in which said connection means further comprises a counterweight operatively connected to said connection means and adapted to retain said pulleys substantially in the plane of movement of the cables.

6. A device according to claim 5, in which said connection means is flat and carries three pulleys in tri angular relation to one another, one single central pulley engaging one pair of cables and two lateral pulleys engaging the other pair.

7. A device according to claim 6, further comprising poles for carrying the cables; one multiple sheave carried by each pole, said multiple sheave comprising four pulleys of larger diameter for the passage of the cables; and one smaller pulley for the passage of the drawing rope.

8. A device according to claim 7, in which the relative position of said four pulleys and of said smaller pulley is such that the radius of the instantaneous rotation of the system on the sheave is longer than the radius of the large pulleys.

9. A device according to claim 7, in which each sheave comprises guiding means for guiding the rope on the pulley, at least one portion of said guiding means being adapted to lift on the passage of said connection means therethrough.

References Cited UNITED STATES PATENTS 2,947,494 8/1960 Merritt 24 2- 156 2,948,483 8/1960 'Petersen 24254 3,037,720 6/ 1962 Leithiser 242- 155 3,276,744 Q0/1966 Cronkright 254--234. 3

O'THELL M. SIMPSON, Primary Examiner. 

